A hair fiber, a keratinous material, contains proteins or polypeptides that are bonded together (cross-linked) by disulfide bonds (—S—S—). A disulfide bond that is formed from the sulfhydryl groups (—SH) of two cysteine residues results in a disulfide-containing cystine amino acid residue. The hair straightening or relaxing process is a chemical process that principally acts by altering cystine disulfide chemical bonds in the hair to form lanthionine, a monosulfide analog of cystine, that can be viewed as being composed of two alanine residues that are cross-linked on their β-carbon atoms by a thioether linkage.
Aqueous alkali containing hair relaxing or straightening compositions are known in the art. Such compositions usually have a pH value of about 12 to 14 due to the presence of one or more of a water-soluble alkali metal or alkaline earth material such as lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide, or a nitrogen base such as guanidinium hydroxide, and are most frequently formulated as emulsified or creamy, viscous preparations so that once applied to the user's (subject's) hair, they will not drip onto the skin or into the eyes.
Hair relaxers are usually supplied as “with base” or “no-base” formulations. A “with base” formulation is generally supplied in two packages; one containing the oleaginous base and one containing a thickened aqueous composition of alkaline materials. For those products with a base, the oleaginous base such as one or more of petrolatum, mineral oil and lanolin is first applied to the user's scalp as a protective layer and hair followed by application of the thickened aqueous alkaline material that then relaxes the hair.
No-base formulations are one package systems in which the aqueous and oleaginous materials are co-emulsified. The no-base formulations are applied directly to the user's hair without a prior pretreatment of the scalp.
One type of no-base hair relaxer formulation contains as the active hair straightening agent an alkali metal hydroxide, typically a caustic base, such as sodium hydroxide or potassium hydroxide. When a relatively low active level of about 1.5 to about 2.5 weight percent of caustic base is used, a protective base is applied only to the hairline to protect the skin around the forehead, ears and neckline, with the remainder of the scalp being directly treated with the relaxer. Such no-base formulations preferably have some of the protective oleaginous material emulsified in an aqueous composition, and are supplied in a “single product” kit.
Most no-base cream products are aqueous emulsions in which water is the continuous phase, i.e., oil-in-water emulsions, because they are easier to rinse from the hair. Instability or de-emulsification can result because of the relatively high concentration of oleaginous material present dispersed in the water phase, which provides a destabilized cream product having two distinctly visible phases. Although such destabilized products can be used, they must be remixed before using in an attempt to assure the user that the active ingredients are at the proper levels in the portion being used. However, such mixing, even though done thoroughly by hand, often does not provide the user with consistent relaxation results, can cause skin irritation or result in increased hair breakage. Product destabilization and resulting consumer dissatisfaction are among the chief complaints in the industry.
A more recently developed type of no-base hair relaxer formulation is commonly called a “no-lye” hair relaxer. With a no-base, no-lye relaxer, a protective base need not be applied to the scalp and can does need to be applied to the hairline. The term “no-lye” means that the active hair straightening agent is an organic chemical base instead of caustic base, although some amount of caustic base can be present.
In commercial practice, the relatively strong organic chemical base, guanidine is usually present in the form of guanidine hydroxide. However, guanidine hydroxide is not generally stable for long periods in aqueous solutions. Consequently, it must be prepared fresh just before using.
Guanidine hydroxide is generally prepared by reacting an inorganic chemical base such as an alkaline earth hydroxide with an aqueous solution of a salt of guanidine, where the anion of this guanidine salt forms a precipitate with the cation of the alkaline earth hydroxide. In commercially available products of this type, the guanidine hydroxide is generally prepared using guanidine carbonate and calcium hydroxide.
When such a no-lye hair relaxer is commercially used, the product is supplied as a two-part kit. One part contains the guanidine carbonate in substantially liquid form and is commonly called the “activator.” The other part contains relatively high amounts of about 4 to about 7 percent calcium hydroxide emulsified in a cosmetic cream base. Prior to using, the consumer or beautician mixes the cream and activator portions of the kit together. The resulting no-lye hair relaxer is then relatively promptly (preferably within 24 hours) applied to the hair. Many of the foregoing emulsion stability problems were overcome in U.S. Pat. No. 4,390,033 and No. 4,237,910 both to our assignee, by the use of certain lipophilic organically-modified hectorite clay gellants. A relatively high amount (about 8 to about 12 weight percent) of the hectorite clay gellant is generally required to achieve a relatively stiff viscous cream.
As noted above, no-base hair relaxers are desirably formulated as emulsified viscous creams so that once applied to the user's hair, they will not drip onto the skin or into the eyes of the person receiving a hair straightening procedure. The cosmetic cream base portion of a no-lye hair relaxer must also mix easily with the activator solution without thinning to a soft runny cream. Additionally, an ideal no-base hair relaxer cream must be easy to remove from the hair at the end of the straightening or relaxer procedure.
A result of a hair no-lye straightening treatment can be that residue of the alkaline composition remains in the hair causing the hair to be dull, stiff, crusty or gritty. For example, when a calcium hydroxide-based product is used in a hair straightening treatment, calcium deposits are left on the hair which leaves a white residue or unattractive “whitening” or “ashing” that remains in the hair because divalent metals like calcium have a relatively good affinity to keratin. A decalcifying shampoo is subsequently needed to remove the ashing. The presence of the calcium deposits also causes the hair have a dry and gritty feeling and a dull appearance. These problems have been at least partially dealt with by use of acidic treatment of the hair as disclosed in U.S. Pat. No. 7,226,585 and No. 7,754,194.
One problem with which the art has not dealt is the discoloration of naturally grey or white hair that is treated with a relaxer composition. That discoloration changes the grey or white hair to colors ranging from yellow, to brown and green tints. The chemical basis for these discolorations is not presently known. The invention disclosed below provides one solution to this problem of discoloration.